activated old iPhone then switched iPhones again w/o backing up old iPhone completely

Greetings Ceebod2019, 

If an iPhone is in setup mode you can start walking through the setup screens and then you’ll come upon a prompt with an option to restore the device from the backup on a computer. If you don’t have a backup, as it seems you are saying, you can choose ‘Don’t Transfer Apps & Data’ to continue with setup. Once set up, you can then sync the available data from Finder/iTunes. 

Here’s an article that can help walk you through the setup screens - Set up your iPhone or iPad

Thanks.